Cystic fibrosis (CF) is still an incurable disease affecting 80,000 people worldwide. Current lack of new CF therapies is due to our poor understanding of disease pathogenesis. Lung complications are responsible for majority of CF mortality. CF airways are characterized by chronic bacterial infections and robust infiltration of leukocytes called neutrophil granulocytes (PMN). PMNs release their granule cargo and DNA to cause lung damage. Although release of neutrophil-derived inflammatory mediators is of high clinical relevance in CF, its mechanism is unknown. The long-term goal of this project is to determine how neutrophils could be manipulated in CF for preventive and therapeutic purposes. The objective in this particular application is to determine the mechanism and clinical relevance of neutrophil extracellular trap (NET) release in CF. The central hypothesis is that NET formation is disadvantageous for the host in CF: NETs cause lung damage without improving microbial clearance. This hypothesis has been formulated based on strong preliminary data produced in the applicant?s laboratory. The rationale for the proposed research is that, once the mechanism and clinical relevance of NET formation in CF will be clear, interfering with it will enable development of innovative PMN/NET-based CF therapies. The central hypothesis will be tested by 1) Determining the complex mechanisms between P. aeruginosa and PMNs/NETs; 2) Determining how NET formation affects pathology and infection in murine models of CF airway disease; and 3) Strengthening the clinical relevance of NETs in CF airway disease using unique CF clinical specimens. This research is innovative because it addresses an understudied but clinically very relevant component of CF airway disease, uses novel tools uniquely developed by the applicant laboratories to quantitate NETs, and employs mouse models that enable a unique mechanistic understanding of the studied process. The proposed research is significant because it focuses on a clinically relevant, unsolved question in CF by using primary human cells, CF clinical samples and animal models. In summary, our proposal will deliver essential knowledge to provide a major impact in the fields of CF airway inflammation, host-microbe interactions and PMN biology. This knowledge can also lead to several potential translational applications.